JP2011113825A - Positive electrode material for lithium-ion secondary battery, and lithium-ion secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode material of high capacity, high output, and superior safety, and a lithium-ion secondary battery using that positive electrode material. <P>SOLUTION: The lithium-ion secondary battery uses the positive electrode material in which a first positive electrode active material expressed by a composition formula Li<SB>x1</SB>Ni<SB>a1</SB>Mn<SB>b1</SB>Co<SB>c1</SB>O<SB>2</SB>(0.2≤x1≤1.2, 0.6≤a1≤0.9, 0.05≤b1≤0.3, 0.05≤c1≤0.3, and a1+b1+c1=1.0) and a second positive electrode active material expressed by a composition formula Li<SB>x2</SB>Ni<SB>a2</SB>Mn<SB>b2</SB>Co<SB>c2</SB>M<SB>d</SB>O<SB>2</SB>(M=Mo, W, 0.2≤x2≤1.2, 0.7≤a2≤0.9, 0.05≤b2≤0.3, 0.05≤c2≤0.3, 0≤d≤0.06, and a2+b2+c2+d=1.0). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a positive electrode material for a lithium ion secondary battery and a lithium ion secondary battery that have a high capacity, high output, and high safety.

  In order to adopt a lithium ion secondary battery as a plug-in hybrid vehicle battery, it is necessary to reduce costs, reduce volume, reduce weight, increase output, etc. while maintaining high safety. The positive electrode material is required to have high capacity, high output, and high safety.

  In Patent Document 1, a positive electrode material containing nickel oxide or second lithium nickel composite oxide is used on the surface of a lithium nickel composite oxide, and safety at the time of an internal short circuit is prevented without hindering high rate characteristics at low temperatures. Increases sex. This positive electrode material has high resistance because the surface of the lithium-nickel composite oxide is coated with high-resistance particles, and obtaining high output as required for plug-in hybrid automobile batteries has further investigation. .

In Patent Document 2, the general formula _{Li v Ni 1-wxyz Co w} Ca x Mg y M z O 2 (M is Mn, Al, B, W, Nb, Ta, In, Mo, Sn, Ti, Zr, from Y It is represented by at least one selected element), and the life characteristics are improved by using a positive electrode material with a larger amount of Ca, Mg, and M on the surface than in the active material. Since this positive electrode material contains an element that does not participate in the reaction, the resistance is high, and obtaining a high output as required for a plug-in hybrid vehicle battery has further studies.

  Patent Document 3 uses a positive electrode material containing one or more kinds of compounds containing an element selected from Mn, W, Nb, Ta, In, Mo, Zr, and Sn on the surface of a lithium nickel composite oxide. Has improved. Since this positive electrode material also contains an element that does not participate in the reaction, the resistance is high, and obtaining a high output as required for a plug-in hybrid vehicle battery has further investigation.

  As described above, in these conventional techniques, further studies are necessary to simultaneously achieve the high capacity, high output, and high safety required for the plug-in hybrid vehicle battery.

JP 2006-302880 A JP 2006-351378 A JP 2006-351379 A

  In order to employ a lithium ion secondary battery as a plug-in hybrid vehicle battery, it is required to have a high capacity, a high output and a high safety.

  In a lithium ion secondary battery, these characteristics are closely related to the properties of the positive electrode material.

In the layered positive electrode material represented by the composition formula LiMO ₂ (M: transition metal), it is necessary to increase the Ni content in the transition metal layer in order to obtain a high capacity.

  However, a positive electrode material having a high Ni content has low structural stability during charging. Therefore, when the battery temperature rises due to battery abuse or the like, oxygen is released from a relatively low temperature and a large exothermic reaction occurs, so it is necessary to consider battery ignition.

  Accordingly, an object of the present invention is to provide a positive electrode material for a lithium ion secondary battery excellent in capacity, output, and thermal stability, and to provide a lithium ion secondary battery excellent in characteristics.

The positive electrode material for a lithium ion secondary battery according to one embodiment of the present invention is
Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 ≦ 0.3, 0.05 ≦ c2 ≦ 0.3, M = Mo, W, 0 ≦ d ≦ 0.06, a2 + b2 + c2 + d = 1.0), a second positive electrode active material,
It is characterized by including.

  The average secondary particle size of the first positive electrode active material is larger than the average secondary particle size of the second positive electrode active material, and the Ni content of the first positive electrode active material is It is preferable that it is below Ni content of a positive electrode active material. Thereby, it is possible to provide a positive electrode material with higher safety.

  Moreover, it is preferable that the mixing ratio of the 1st positive electrode active material contained in positive electrode material shall be 30 to 70% by mass percentage.

  Moreover, it is preferable that the average secondary particle diameter of a 2nd positive electrode active material is 1/2 or less of the average secondary particle diameter of a 1st positive electrode active material.

  Further, the Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.8, and the Ni content a2 of the second positive electrode active material is 0.75 ≦ a2 ≦ 0.8. Is preferred.

  Further, such a positive electrode material for a lithium ion secondary battery is used as a positive electrode of a lithium ion secondary battery in which a positive electrode capable of occluding and releasing lithium and a negative electrode capable of occluding and releasing lithium are formed via a nonaqueous electrolyte and a separator. be able to.

  According to the present invention, a positive electrode material for a lithium ion secondary battery excellent in capacity, output, and thermal stability can be obtained, and a lithium ion secondary battery excellent in characteristics can be provided.

The schematic diagram which shows the mixed state of two types of positive electrode active materials. Sectional drawing which shows a lithium ion secondary battery.

  The characteristics of the present invention will be described below based on the present embodiment.

The positive electrode material of this example has the composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂ (0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3). , 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) and a composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d O ₂ (0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 ≦ 0.3, 0.05 ≦ c2 ≦ 0.3, M = Mo, W, 0 ≦ d ≦ 0.06, a2 + b2 + c2 + d = 1.0) and the second positive electrode active material.

  The high Ni content positive electrode active material to which Mo and W are added according to this example has a high Ni content in which the amount of oxygen released when the temperature rises after desorption of lithium does not contain Mo and W. Compared to the amount of positive electrode active material, it is less than half.

  Therefore, when the battery is heated, the positive electrode active material is mixed with the high Ni content positive electrode active material to which Mo and W are not added, and the high Ni content positive electrode active material to which Mo and W are added. Since the amount of oxygen released from the inside can be reduced, it is possible to provide a positive electrode material for a lithium ion secondary battery that is less likely to cause ignition when heated.

  Furthermore, the average secondary particle size of the first positive electrode active material is made larger than the average secondary particle size of the second positive electrode active material. Since Mo and W are added to the second positive electrode active material, the resistance increases. Therefore, to adopt as a plug-in hybrid vehicle battery, the average secondary particle size of the second positive electrode active material is made smaller than the average secondary particle size of the first positive electrode active material, and the lithium diffusion distance is shortened. There is a need to.

  Further, the mixing ratio of the first positive electrode active material contained in the positive electrode material is set to 30 to 70% by mass percentage. When the ratio is less than 30%, the capacity decreases. When the ratio is more than 70%, the amount of oxygen released from the positive electrode active material increases due to the temperature rise, which causes a safety problem.

  In addition, the average secondary particle size of the second positive electrode active material is set to not more than one half of the average secondary particle size of the first positive electrode active material. This is because the filling rate of the positive electrode material is improved by reducing the particle size.

  Further, the Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.8, and the Ni content a2 of the second positive electrode active material is 0.75 ≦ a2 ≦ 0.8. This is because a high-capacity positive electrode material can be provided by increasing the Ni content in the transition metal layer.

  Then, the Ni content of the first positive electrode active material is made smaller than the Ni content of the second positive electrode active material.

  Then, using such a positive electrode material, a positive electrode capable of occluding and releasing lithium is formed through a nonaqueous electrolyte and a separator together with a negative electrode capable of occluding and releasing lithium, whereby a lithium ion secondary battery can be configured.

In the embodiment of the present invention, as the positive electrode material,
Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂ (0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0 .3, a1 + b1 + c1 = 1.0) and a composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d O ₂ (0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 ≦ 0.3, 0.05 ≦ c2 ≦ 0.3, M = Mo, W, 0 ≦ d ≦ 0.06, a2 + b2 + c2 + d = 1.0) A material mixed with the second positive electrode active material is used.

  Here, the amount of Li in the first positive electrode active material is 0.2 ≦ x1 ≦ 1.2. This is because when x1 <0.2, the amount of Li present in the Li layer in the charged state is This is because the layered crystal structure cannot be maintained. In addition, when 1.2 <x1, the amount of transition metal in the composite oxide decreases, and the capacity decreases.

  The amount of Ni is 0.6 ≦ a1 ≦ 0.9. This is because the content of Ni mainly contributing to the charge / discharge reaction decreases and the capacity decreases when a1 <0.6. .

  The amount of Mn is 0.05 ≦ b1 ≦ 0.3. However, when b1 <0.05, the structure in the charged state becomes unstable, and the oxygen release temperature from the positive electrode decreases. This is because when b1> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is reduced and the capacity is reduced.

  The amount of Co is 0.05 ≦ c1 ≦ 0.3. However, when c1 <0.05, the structure in the charged state becomes unstable, and the volume change of the positive electrode active material during charge / discharge increases. When c1> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is reduced, and the capacity is reduced.

  Here, the amount of Li in the second positive electrode active material is 0.2 ≦ x2 ≦ 1.2. This is because when x2 <0.2, the amount of Li present in the Li layer in the charged state is This is because the layered crystal structure cannot be maintained. Further, when 1.2 <x2, the amount of transition metal in the composite oxide is decreased, and the capacity is decreased.

  The amount of Ni is 0.7 ≦ a2 ≦ 0.9. This is because, when a2 <0.7, the content of Ni mainly contributing to the charge / discharge reaction is decreased and the capacity is decreased. .

The amount of Mn is 0.05 ≦ b2 ≦ 0.3. However, when b2 <0.05, the structure in the charged state becomes unstable, and the oxygen release temperature from the positive electrode decreases. This is because when b2> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is reduced and the capacity is reduced.

  The amount of Co is 0.05 ≦ c2 ≦ 0.3. However, when c2 <0.05, the structure in the charged state becomes unstable, and the volume change of the positive electrode active material during charge / discharge increases. This is because, when c2> 0.3, the content of Ni mainly contributing to the charge / discharge reaction is reduced and the capacity is reduced.

  The amount of M is 0 ≦ d ≦ 0.06. This is because, when d> 0.06, the content of Ni mainly contributing to the charge / discharge reaction is decreased, and the capacity is decreased.

(Preparation of positive electrode active material)
Nickel oxide, manganese dioxide, cobalt oxide, molybdenum oxide, and tungsten oxide were used as raw materials, weighed so as to have a predetermined atomic ratio, and then added with pure water to form a slurry.

  The slurry was pulverized with a zirconia bead mill until the average particle size became 0.2 μm.

  A polyvinyl alcohol (PVA) solution was added to this slurry in an amount of 1 wt.% In terms of the solid content ratio, further mixed for 1 hour, and granulated and dried by a spray dryer.

  Lithium hydroxide and lithium carbonate were added to the granulated particles so that the Li: (NiMnCo) ratio was 1.05: 1.

  Next, this powder was fired at 850 ° C. for 10 hours to have a layered structure crystal, and then pulverized to obtain a positive electrode active material 1-1 (see Table 1).

  Further, coarse particles having a particle size of 30 μm or more were removed by classification, and then used for electrode production.

  Further, the method for producing the positive electrode active material in this example is not limited to the above method, and other methods such as a coprecipitation method may be used.

  The composition ratios of the transition metals of the synthesized first positive electrode active material and second positive electrode active material are shown in Tables 1 and 2 below, respectively.

  In Table 1 (first positive electrode active materials 1-1 to 1-4) and Table 2 (second positive electrode active materials 2-1 to 2-11), the synthesized first positive electrode active materials (Ni , Mn, Co) and the second positive electrode active material (Ni, Mn, Co, Mo, W), and the average secondary particle diameter.

  The positive electrode active material 1-1 and the carbon-based conductive agent were weighed so as to have a mass ratio of 85: 10.7, and the active material and the conductive agent were combined using mechanofusion. Here, the active material and the conductive agent may be combined using a device such as a hybridizer.

  The same operation was performed on the positive electrode active material 2-1.

  Next, the two types of composite materials were mixed at a mass ratio of 40:60. By this method, the conductive agent can be highly dispersed on the surface of each active material, and the surface of the particles can be coated with the conductive agent.

  The positive electrode material thus formed is composed of secondary particles 1 of the first positive electrode active material and secondary particles of the second positive electrode active material, as shown in the schematic diagram showing the mixed state of the two types of positive electrode active materials in FIG. Particles 2 are mixed.

  As shown in FIG. 1, the secondary particles 2 of the second positive electrode active material are formed smaller than the secondary particles 1 of the first positive electrode active material.

  Since the electron conductivity is improved by the coating of the conductive agent, a high capacity is maintained even when a large current is passed when used as a positive electrode material.

  In addition, since a conductive agent exists between the active materials when mixing different active materials, a conductive network is formed between the active materials, which may reduce the proportion of isolated active materials that do not contribute to the charge / discharge reaction. And high capacity can be maintained.

  On the other hand, when two active materials and a conductive agent are mixed without compounding the active material and the conductive agent, the surface of each active material is not coated with the conductive agent, resulting in a decrease in electronic conductivity. To do.

  Furthermore, the mixed state of each active material and the conductive agent is deteriorated, it becomes difficult to form a conductive network between the active materials, the ratio of the isolated active material is increased, and the capacity is decreased.

  Thereafter, a mixed material of two kinds of active materials and a conductive agent and a binder dissolved in NMP were mixed so that the mixed material and the binder were in a mass ratio of 95.7: 4.3.

The uniformly mixed slurry was applied onto an aluminum current collector foil having a thickness of 20 μm, dried at 120 ° C., and compression-molded with a press so that the electrode density was 2.7 g / cm ³ .

  Thereafter, it was punched into a disk shape having a diameter of 15 mm to produce a positive electrode.

Prototype battery using prepared positive electrode, metallic lithium as negative electrode, and non-aqueous electrolyte (1.0 mol / liter LiPF ₆ dissolved in a 1: 2 mixed solvent by volume ratio of EC and DMC) Was made.

  In the test battery according to the present invention, the conductive agent, the binder, the negative electrode, the electrolytic solution, and the electrolyte to be used are not limited to those described above. For example, the following may be used.

  Examples of the conductive agent include graphite, acetylene black, and carbon black.

  Examples of the binder include polytetrafluoroethylene and a rubber binder.

  Examples of the electrolytic solution include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, tetrahydrofuran, and dimethoxyethane.

Examples of the electrolyte include LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

  Table 3 shows the mixing ratio of the first positive electrode active material and the second positive electrode active material.

  Table 3 shows Example 1 to Example 13 and Comparative Example 1 to Comparative Example 10.

  The first positive electrode active material shown in Table 3 is shown in Table 1, and the second positive electrode active material is shown in Table 2. The mixing ratio shown in Table 3 is the mixing ratio of these first positive electrode active material and second positive electrode active material.

(Charge / discharge test)
Next, the following tests were performed using the prototype battery described above.

  The charge rate was set to 0.1 C, and the battery was charged at a constant current / constant voltage up to 4.3 V, and then discharged at a constant current up to 2.5 V at 0.1 C.

(Differential scanning calorimetry)
Also, after charging to 4.3 V at a constant current / constant voltage, the electrode was taken out from the test battery, washed with DMC, punched into a disk shape with a diameter of 3.5 mm, placed in a sample pan, 1 μl of electrolyte was added and sealed. .

  The heat generation behavior when this sample was heated at 5 ° C./min was examined.

(DC resistance measurement)
Furthermore, the electrode resistance at room temperature was measured using a test battery. Constant current discharge was performed when the open circuit voltage of the test battery was in the range of 3.7 V to 4.4 V, and the voltage at the time of discharge was recorded at intervals of 0.1 seconds.

  Next, the voltage drop at 10 seconds from the open circuit voltage was measured to determine the electrode resistance.

  In Example 2, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-2 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 3, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-3 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 4, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-4 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 5, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-5 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 6, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-6 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 7, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-2 and 2-1 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 8, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-3 and 2-1 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 9, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-2 and 2-8 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 10, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-2 and 2-9 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 11, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-8 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 12, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-1 were mixed at a mass ratio of 30:70 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 13, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-1 were mixed at a mass ratio of 50:50 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 14, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-1 were mixed at a mass ratio of 70:30 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  In Example 15, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-10 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 1]
In Comparative Example 1, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active material 1-2 was used as a positive electrode active material, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 2]
In Comparative Example 2, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active material 1-1 was used as the positive electrode active material, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 3]
In Comparative Example 3, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active material 2-1 was used as the positive electrode active material, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 4]
In Comparative Example 4, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-7 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 5]
In Comparative Example 5, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active material 1-3 was used as the positive electrode active material, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 6]
In Comparative Example 6, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-4 and 2-8 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 7]
In Comparative Example 7, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-2 and 2-9 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 8]
In Comparative Example 8, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-1 were mixed at a mass ratio of 20:80 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 9]
In Comparative Example 9, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-1 were mixed at a mass ratio of 80:20 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

[Comparative Example 10]
In Comparative Example 10, a prototype battery was produced in the same manner as in Example 1 except that the produced positive electrode active materials 1-1 and 2-11 were mixed at a mass ratio of 40:60 and used as the positive electrode active material. Were prepared, and a charge / discharge test and a DSC measurement were performed.

  Tables 4 to 7 show the capacity ratio, the calorific value ratio, and the resistance ratio for Examples 1 to 15 and Comparative Examples 1 to 10, respectively.

  Tables 4 to 7 show values obtained by dividing the initial discharge capacity values obtained in Examples 1 to 6, 12 to 15 and Comparative Examples 1 to 4 and 8 to 10 by the initial discharge capacity values of Comparative Example 1. In Examples 7 to 11 and Comparative Examples 5 to 7, values obtained by dividing the obtained initial discharge capacity values by the initial discharge capacity values of Comparative Example 5 are shown.

  In Tables 4 to 7, the calorific value obtained in Examples 1 to 6, 12 to 15 and Comparative Examples 1 to 4 and 8 to 10 was divided by the initial discharge capacity value of Comparative Example 1. The values are obtained by dividing the calorific value obtained in Examples 7 to 11 and Comparative Examples 5 to 7 by the initial discharge capacity value of Comparative Example 5.

  In Tables 4 to 7, the values of the electrode resistance obtained in Examples 1 to 6, 12 to 15 and Comparative Examples 1 to 4 and 8 to 10 were divided by the initial discharge capacity value of Comparative Example 1. The values obtained by dividing the electrode resistance values obtained in Examples 7 to 11 and Comparative Examples 5 to 7 by the initial discharge capacity values in Comparative Example 5 are shown.

  Examination of the results shown in Table 4 revealed that the discharge capacities in Examples 1 to 6 were larger than Comparative Example 1. This is presumably because the positive electrode active materials selected in Examples 1 to 6 have a high Ni content in the transition metal layer.

  Moreover, it became clear that the emitted-heat amount in Examples 1-6 shows a value smaller than the comparative example 1. FIG. This is because Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added. Moreover, although the resistance increased, the rate of increase was 10% or less.

  On the other hand, in Comparative Examples 1 to 4, compared with Comparative Example 1, it was impossible to achieve both an increase in capacity and a reduction in calorific value. In Comparative Example 2, since only the first positive electrode active material was present, the calorific value was increased. In Comparative Example 3, since only the second positive electrode active material was present, the capacity decreased. In Comparative Example 4, the capacity decreased because 8% of Mo was present in the second positive electrode active material.

  Examination of the results shown in Table 5 revealed that the discharge capacities in Examples 7 to 11 were larger than Comparative Example 6. This is presumably because the positive electrode active materials selected in Examples 7 to 11 have a high Ni content present in the transition metal layer.

  It became clear that the calorific value in Examples 7-11 shows a value smaller than Comparative Example 6. This is because Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added. Moreover, although the resistance increased, the rate of increase was 10% or less.

  On the other hand, in Comparative Examples 5 to 7, compared with Comparative Example 5, it was impossible to achieve both an increase in capacity and a reduction in calorific value. In Comparative Example 6, since the Ni content of the first positive electrode active material is as low as 50%, the capacity is low. In Comparative Example 7, since the Ni content of the second positive electrode active material is as low as 60%, the capacity is low. The second positive electrode active material is excellent in thermal stability because it contains Mo and W which have the effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised. Therefore, the Ni content can be increased. In order to achieve both high capacity and high safety, a second positive electrode active material in which the Ni content is higher than that of the present material and Mo and W are added to the first positive electrode active material is required.

  Examination of the results shown in Table 6 and Table 4 revealed that the discharge capacities in Examples 1 and 12 to 14 were larger than Comparative Example 1. This is presumably because the positive electrode active materials selected in Examples 1 and 12 to 14 have a high Ni content present in the transition metal layer.

  Moreover, it became clear that the emitted-heat amount in Example 1, 12-14 shows a value smaller than the comparative example 1. FIG. This is because Mo and W having an effect of reducing the amount of oxygen released from the positive electrode active material when the temperature is raised are added. Moreover, although the resistance increased, the rate of increase was 10% or less.

  On the other hand, in Comparative Examples 2, 3, 7, and 8, compared with Comparative Example 1, it was impossible to achieve both an increase in capacity and a reduction in heat generation. In Comparative Examples 2 and 8, the mixing ratio of the first positive electrode active material was large and the calorific value was large, and in Comparative Examples 3 and 7, the mixing ratio of the second positive electrode active material was large and the capacity was reduced.

  Considering the results shown in Table 7 and Table 4, compared with Comparative Example 1, Examples 1 and 15 achieved both increased capacity and reduced heat generation, and the rate of increase in resistance was 10% or less.

  On the other hand, in Comparative Example 10, as compared with Comparative Example 1, the rate of increase in resistance was as large as 10.8%. This was because the secondary cathode diameter of the second positive electrode active material was large, and the rate of increase in resistance could not be reduced.

  FIG. 2 is a cross-sectional view showing a lithium ion secondary battery.

  The lithium ion secondary battery shown in FIG. 2 has a positive electrode plate 11 coated with a positive electrode material on both sides of a current collector and a negative electrode plate 12 coated with a negative electrode material on both sides of the current collector through a separator 13. These are formed by winding.

  Such a wound body is inserted into the battery can 14. Then, the negative electrode plate 12 is electrically connected to the battery can 14 via the negative electrode lead piece 15.

  Further, the sealing lid portion 16 is formed on the battery can 14 via the packing 18. Then, the positive electrode plate 11 is electrically connected to the sealing lid portion 16 via the positive electrode lead piece 17.

  The wound body is insulated by the insulating plate 19.

  By using the material shown in this embodiment as the positive electrode material of the lithium ion secondary battery, a lithium ion secondary battery excellent in capacity, output, and thermal stability can be provided.

  The present invention is particularly promising as a positive electrode material for lithium ion secondary batteries for plug-in hybrid vehicles.

DESCRIPTION OF SYMBOLS 1 Secondary particle of 1st positive electrode active material 2 Secondary particle of 2nd positive electrode active material 11 Positive electrode plate 12 Negative electrode plate 13 Separator 14 Battery can 15 Negative electrode lead piece 16 Sealing cover part 17 Positive electrode lead piece 18 Packing 19 Insulating plate

Claims (7)

Composition formula Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂
(0.2 ≦ x1 ≦ 1.2, 0.6 ≦ a1 ≦ 0.9, 0.05 ≦ b1 ≦ 0.3, 0.05 ≦ c1 ≦ 0.3, a1 + b1 + c1 = 1.0) A first positive electrode active material,
Composition formula Li _x2 Ni _a2 Mn _b2 Co _c2 M _d O ₂
(0.2 ≦ x2 ≦ 1.2, 0.7 ≦ a2 ≦ 0.9, 0.05 ≦ b2 ≦ 0.3, 0.05 ≦ c2 ≦ 0.3, M = Mo, W, 0 ≦ d ≦ 0.06, a2 + b2 + c2 + d = 1.0), a second positive electrode active material,
A positive electrode material for a lithium ion secondary battery, comprising: In claim 1,
A positive electrode material for a lithium ion secondary battery, wherein an average secondary particle size of the first positive electrode active material is larger than an average secondary particle size of the second positive electrode active material. In claim 1,
The positive electrode material for a lithium ion secondary battery, wherein the content of Ni in the first positive electrode active material is equal to or less than the content of Ni in the second positive electrode active material. In claim 1,
A positive electrode material for a lithium ion secondary battery, wherein a mixing ratio of the first positive electrode active material contained in the positive electrode material is 30 to 70% by mass percentage. In claim 1,
The positive electrode material for a lithium ion battery, wherein an average secondary particle size of the second positive electrode active material is not more than one half of an average secondary particle size of the first positive electrode active material. In claim 1,
The Ni content a1 of the first positive electrode active material is 0.7 ≦ a1 ≦ 0.8, and the Ni content a2 of the second positive electrode active material is 0.75 ≦ a2 ≦ 0.8. A positive electrode material for a lithium ion battery. In a lithium ion secondary battery in which a positive electrode capable of occluding and releasing lithium and a negative electrode capable of occluding and releasing lithium are formed via a nonaqueous electrolyte and a separator,
A lithium ion secondary battery comprising the positive electrode material for a lithium ion secondary battery according to claim 1.

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